This invention relates generally to audio speaker systems, and particularly to audio speaker systems of the type which include one or more middle frequency range drivers or squakers mounted on a flat baffle, and one or more low frequency range drivers or woofers.
Audio speaker systems today frequently employ a plurality of speakers or drivers individually constructed for response to diverse audio frequency ranges. Such a system may, for example, employ a low-range driver or woofer, a mid-range driver or squaker which sometimes is referred to as a mid-range tweeter, and a high-range driver or tweeter. The upper end portion of the frequency response range of the woofer is selected to overlap the lower end portion of the squaker in order to achieve sufficient response throughout their combined ranges. Similarly, the upper end portion of the squaker range is selected to overlap the lower portion of the tweeter range. Within these overlapping or crossover frequency ranges response dropoff of each speaker must be so controlled as to produce substantially level response in the aggregate. Otherwise, at crossover frequencies the system would produce an output volume differing, usually to excess, from that of the other frequencies.
To shape the frequency response curves of the various system drivers electronic circuits have heretofore been devised generally referred to as crossover networks. Exemplary of such networks are those disclosed in U.S. Pat. Nos. 2,612,558, 2,832,828, 3,457,370, 3,383,215 and 3,895,193.These circuits have comprised a number of electronic components connected in circuit with the audio signal circuit that couples the drivers with the signal output amplifiers. Typically, these networks have included one or more inductors in series circuit with one or more drivers, and one or more capacitors in parallel therewith. For example, with an inductor placed in series with a woofer the acoustic output of the woofer can be made to provide an energy output level of -3 db at nominal crossover frequencies with a filter slope of 6 db per octave. With a capacitor placed in series circuit with the system squaker an energy level of -3 db can also be achieved at that frequency with a filter slope of 6 db per octave. The provision of series resonant circuits in the network can insure smooth circuit impedance throughout crossover. Such impedance correction networks are usually required to compensate for variations between designed and actual load impedances of the driver for which the frequency balancing network is itself designed.
The combination of the just described networks is cumulatively productive of fairly complex and expensive circuitry. That audio frequency and wavelength are axiomatically related has heretofore led others to seek mechanical means, usually involving the spacing of speakers or dimensioning of audio transmission lines therebetween to harmonize multiple drivers in a single system. These approaches however, as evidenced by U.S. Pat. Nos. 3,155,774, 3,165,587 and 3,727,004, have not completely eliminated the need for crossover networks. In audio systems having a woofer and a flat baffle squaker from both sides of which soundwaves are propagated substantially unbaffled, a mechanical approach towards eliminating or simplifying crossover networks have been apparently unfeasible. The present invention nevertheless is directed to just such a development.
Accordingly, general objects of the invention are to provide improved audio speaker systems and methods for balancing frequency crossover between system component speakers.
More specifically, it is an object of the invention to provide an improved method of balancing frequency crossover of an audio speaker system having a flat baffle mid-range speaker and a low-range speaker.
Another object of the invention is to provide a method of dimensioning a flat baffle supporting a mid-range speaker for audio system use with a low-range speaker.
Another object of the present invention is to provide an improved audio speaker system of the type having a mid-range speaker mounted on a flat baffle and a low-range speaker.
Another object of the invention is to provide an audio speaker system of the type just described with improved, relatively simple and economic frequency crossover balancing means.
Yet another object of the invention is to provide an audio speaker system of the type described which exhibits minimal phase shift between speakers.